Method for controlling a cycle-skipping control system including computer readable code and controller for performing such method

Abstract

A method, computer-readable code, and controller are provided for controlling a cycle-skipping control system having two or more cycle skippers connected to a common multi-phase AC (alternating current) power source to drive a variable frequency load. A respective firing sequence is generated to be applied to a plurality of power switches in the two or more cycle skippers for implementing a desired mode of operation. A phase angle shift is provided between each respective firing sequence to be applied to the two or more cycle skippers over a firing cycle. This enables a non-concurrent firing for each cycle skipper over the firing cycle.

1. A method for controlling a cycle-skipping control system comprising two or more cycle skippers connected to a common multi-phase AC (alternating current) power source to drive a variable frequency load, said method comprising:
 selecting a desired mode of operation for the cycle-skipping control system; 
 generating a respective firing sequence to be applied to a plurality of power switches in the two or more cycle skippers for implementing the desired mode of operation; and 
 providing a predefined phase angle shift between each respective firing sequence to be applied to the two or more cycle skippers over a firing cycle, wherein said phase angle shift enables a non-concurrent firing for each cycle skipper over the firing cycle. 
 
   
   
     2. The method of  claim 1  wherein said phase angle shift is symmetrically distributed over the firing cycle, thereby optimally reducing harmonic components in currents supplied by the common power source. 
   
   
     3. The method of  claim 1  wherein said phase angle shift is asymmetrically distributed over the firing cycle, thereby reducing harmonic components in currents supplied by the common power source. 
   
   
     4. The method of  claim 1  wherein the selecting of said mode of operation comprises selecting a fraction 1/N of an input frequency source to be supplied at one or more output terminals by the cycle-skipping control system, where N is a predetermined integer. 
   
   
     5. The method of  claim 1  wherein the selecting of said mode of operation comprises selecting at least one of the following: a first phase sequence, and a second phase sequence, wherein the second phase sequence comprises a sequence reversal with respect to the first phase sequence. 
   
   
     6. The method of  claim 1  wherein the selecting of said mode of operation comprises selecting at least one of the following: a positive portion of an input voltage source and a negative portion of the input voltage source. 
   
   
     7. An article of manufacture comprising a computer program product comprising a computer-usable medium having a computer-readable code therein for controlling a cycle-skipping control system comprising two or more cycle skippers connected to a common multi-phase AC (alternating current) power source to drive a variable frequency load, said computer-readable code comprising:
 computer-readable code for selecting a desired mode of operation for the cycle-skipping control system; 
 computer-readable code for generating a respective firing sequence to be applied to a plurality of power switches in the two or more cycle skippers for implementing the desired mode of operation; and 
 computer-readable code for providing a predefined phase angle shift between each respective firing sequence to be applied to the two or more cycle skippers over a firing cycle, wherein said phase angle shift enables a non-concurrent firing for each cycle skipper over the firing cycle. 
 
   
   
     8. The article of manufacture of  claim 7  wherein said phase angle shift is symmetrically distributed over the firing cycle, thereby optimally reducing harmonic components in currents supplied by the common power source. 
   
   
     9. The article of manufacture of  claim 7  wherein said phase angle shift is asymmetrically distributed over the firing cycle, thereby reducing harmonic components in currents supplied by the common power source. 
   
   
     10. The article of manufacture of  claim 7  wherein the computer-readable code for selecting the mode of operation comprises code for selecting a fraction 1/N of an input frequency source to be supplied at one or more output terminals by the cycle-skipping control system, where N is a predetermined integer. 
   
   
     11. The article of manufacture of  claim 7  wherein the computer-readable code for selecting the mode of operation comprises code for selecting at least one of the following: a first phase sequence, and a second phase sequence, wherein the second phase sequence comprises a sequence reversal with respect to the first phase sequence. 
   
   
     12. The article of manufacture of  claim 7  wherein the computer-readable code for selecting the mode of operation comprises selecting at least one of the following: a positive portion of an input voltage source and a negative portion of the input voltage source. 
   
   
     13. A controller for a cycle-skipping control system comprising two or more cycle skippers connected to a common multi-phase AC (alternating current) power source to drive a variable frequency load, said controller comprising:
 a mode selector for selecting a desired mode of operation for the cycle-skipping control system; 
 a sequence generator for generating a respective firing sequence to be applied to a plurality of power switches in the two or more cycle skippers for implementing the desired mode of operation; and 
 a phase angle shifter for providing a predefined phase angle shift between each respective firing sequence to be applied to the two or more cycle skippers over a firing cycle, wherein said phase angle shift enables a non-concurrent firing for each cycle skipper over the firing cycle. 
 
   
   
     14. The controller of  claim 13  wherein the power source comprises a three-phase power source. 
   
   
     15. The controller of  claim 13  wherein the variable frequency load comprises one or more induction motors. 
   
   
     16. The controller of  claim 13  wherein the power source comprises a three-phase locomotive power source and the variable frequency load comprises one or more induction motors onboard the locomotive. 
   
   
     17. The controller of  claim 13  wherein said phase angle shift is symmetrically distributed over the firing cycle, thereby optimally reducing harmonic components in currents supplied by the common power source. 
   
   
     18. The controller of  claim 13  wherein said phase angle shift is asymmetrically distributed over the firing cycle, thereby reducing harmonic components in currents supplied by the common power source. 
   
   
     19. The controller of  claim 13  wherein the phase shifter is responsive to a common synchronization signal for the cycle skippers. 
   
   
     20. The controller of  claim 13  wherein the phase shifter is responsive to at least one of the following: a monitored parameter of source voltages, a monitored parameter of source currents, a monitored parameter of load currents, a monitored parameter of the power source, a parameter indicative of a cycle skipper firing state and a combination of the foregoing. 
   
   
     21. The controller of  claim 20  wherein the monitored parameter of source voltages and currents comprises at least one of the following parameters: frequency variation, zero crossings, phase angle variation, and a combination of the foregoing parameters. 
   
   
     22. The controller of  claim 20  wherein the power source comprises an alternator and the monitored parameter of the power source comprises at least one of the following parameters: alternator shaft speed, alternator shaft position and a combination of the foregoing parameters.